Seeds tumble as Zhang withdraws from Tianjin Open
Only three seeds remain after Tuesday's first-round action at the Tianjin Open, with Elena Vesnina, Timea Babos and Yaroslava Shvedova crashing out, while Zhang Shuai has withdrawn with a back problem.
Sixth seed Yulia Putintseva had already been eliminated on Monday, leaving Svetlana Kuznetsova and Monica Puig as the only seeded players successfully into the second round.
Top seed and defending champion Agnieszka Radwanska takes on Tatjana Maria in her first-round tie on Wednesday.
Vesnina fell to qualifier Shelby Rogers in a 7-5 4-6 7-6 (7-4) defeat, while Babos' campaign was ended by another American - 2014 winner Alison Riske coming from behind to win 2-6 6-4 6-3.
Shvedova was seen off in straight sets by Naomi Osaka, but Puig suffered no such fate against her Japanese opponent.
The Olympic gold medallist triumphed 6-4 7-6 (7-5) against Kurumi Nara to set up a second-round clash with Spain's Lara Arruabarrena, who knocked out Liu Fangzhou.
Elsewhere, there were wins for Magda Linette, Xinyun Han and Evgeniya Rodina against Nina Stojanovic, Yifan Xu and Christina McHale respectively.
Zhang's withdrawal saw Peng Shuai earn a bye to the next round.